Most HIV transmissions occur mucosally, including mother-to-child transmission (MTCT). As HIV clade C predominates worldwide, we initially focused on immunoprevention of HIV clade C MTCT. We identified a quadruple (4x) combination of human neutralizing monoclonal antibodies (nmAbs) that, although raised against clade B, was broadly reactive across clades, including clade C. To test the 4 nmAbs in vivo, we constructed several simian-human immunodeficiency viruses encoding env of primary R5 HIV clade C strains (termed SHIVenvC's). The 4x nmAb combination prevented infection in 3 out of 4 monkey infants, whereas all controls had high peak viremia after oral SHIVenvC challenge. While we provided compelling evidence for the protective role of nAbs, we and others were stunned by findings that some of these 4 nmAbs are auto-antibodies. We re-oriented our HIVRAD goals as there is a great need to find new targets for nmAb responses, especially against HIV clade C. This re-competition has three main goals: 1. To refine the SHIVenvC primate model for mucosal transmission by increasing the virulence of R5 SHIVenvC's, generating a fully heterologous SHIVenvC, and by comparing the molecular evolution of HIV clade C env in infected African mother/infant pairs and in rhesus monkeys infected with SHIV's harboring homologous HIV clade C env genes. 2. To harness the broadly reactive humoral immune responses of monkeys infected with SHIVenvC's whose sera neutralize divergent HIV clade C and B strains. Using B cells of such monkeys, we seek to isolate nmAbs, determine epitope specificities, and exploit random peptide phage-display libraries to identify mimotopes to the novel rhesus nmAb epitopes, both linear and conformational (via a novel computer program). We will also directly use phage display with polyclonal IgG with broadly reactive nAb responses. 3. To test the new concept of SEquential Editing and Focusing of Antibody Responses (SEEFAR). We postulate that the variable (V) loops in Env attract most of the nmAb responses, which predominantly target individual virus types. We seek to avoid boosting such narrow, type-specific nAb responses by developing Env immunogens deleted in most/all V loops, and/or sequentially editing out type-specific nAb responses by boosting with immunogens that do not share V-loop epitopes. The SEEFAR strategy will be tested in the context of a replication-competent adenovirus prime/recombinant protein boost. Some of the reagents and vaccine strategies proposed can be entered directly into future clinical trials, and insights gained from analyzing broadly reactive nmAbs will provide important new structural information for the subsequent design of improved immunogens. Lastly, fine-tuning the SHIVenvC primate model will allow testing candidate anti-HIV clade C AIDS vaccines in a relevant mucosal challenge system.